of that. ♪ magnificent harlem gospel choir. That's the theme song from one of our favorite movies, "vacation." Perfect overture for our all-star reunion blowout. Cameron mathison, you're starting us off today. I do. And it was -- the cast reunion. But I have to tell you guys, it felt a lot more like a family gathering. This was an extremely funny family. The cast, chevy chase, beverly d'angelo, and michael anthony hall. They have a family vibe after all these years. Taking the kids crosscountry, this is the vehicle you should be using. Reporter: It's one of the funniest comedies of all-time. Why aren't we flying? Because getting there is half the fun. You know that. Reporter: And it screams 1980s AMERICA. "Vacation." She was born without a tongue, clark. Don't you worry about her. She whistles like a bird and eats like a horse. When they close the road they put up big signs, like this one. Reporter: The story of the griswold family, on their epic cross-country quest to get to wally world. We're closed for two weeks to clean and repair america's favorite family fun park. Reporter: Now, a reunion with the original cast 30 years in the making. Chevy chase, beverly d'angelo, anthony michael hall, and dana barron. One thing is immediately clear. This crew is downright funny. They're doing a gag. You can't fool me, buddy. I know you're taping. Reporter: Watching you guys, it's like the chemistry never stops. You had so much fun at the photo shoot. Nothing. Now, we are starting. Reporter: Right now? What's also clear is that I'm just along for the ride. Is this what it was like on-set, shooting "vacation"? On some level? Tell me about it. I don't remember anything. For me, it was laughter and listening. And my goodness, did he just say that? It was a family experience for me. We were on vacation together. By the way, we were driving. Literally. Filmed this cross-country. We had a place to play. Must have passed away somewhere near flagstaff. You want me to strap her to the hood? What's the difference? She'll be fine. Not like it's going to rain or something. Reporter: Much of that comedic family atmosphere, they credit to harold ramis, who welcome d ad-libbing on the set. Bow your head. Hallelujah. Clark? Honey, I'm not an ordained minister. I'm doing my best. Okay? Reporter: Was that written? Or was it -- it's just harold saying, try Reporter: Slap yourself in the face with the baloney sandwich seduction dance. How did that come about? It just came about. That's just him. She's dancing to some music coming out of her car. And I have the sandwich. And I started to dance a little. Reporter: Like the bow loney. A young anthony michael hall's career was about to launch. This movie gave me a start in everything. And I remember laughing and having a great experience the whole summer. When I was your age, my dad shared a beer with me. And I thought it was about the best thing in the world. Reporter: I could tell it wasn't his first beer he drank. I remember that take. Michael kept drinking and drinking. Everybody just lit up and went -- got it. Yeah, fun. Reporter: And underneath all the comic asides, there's an unmistakable feeling of family here. Chevy's a genius and my dear friend. And I'm so glad that the four of us can all be together at the same time. It was a special time. You hope that you can touch somebody's life in some way. And you don't think you're going to do it, unless you're getting an oscar for it. I did it for the gr and for the chinese. Reporter: All that's good must end. But a "vacation" reunion wouldn't be complete without a little mockingbird. ♪ Mockingbird everybody have you heard ♪ ♪ have you heard if that diamond ring don't shine ♪ ♪ don't shine going to buy me a diamond ring ♪ ♪ going to buy you a diamond ring ♪ that was awesome. Sorry, folks. Park's closed. The moose out front should have told you. Reporter: I did find out there was an alternative ending. The original ending had them taking the wally world president captive at gunpoint and forcing him to ride all of the rides, which didn't go well with the audience. They reshot it six months later. And michael anthony hall had grown six inches. So, they had to reshoot it. That original ending sounds a little dark, frankly. Inspired idea to bring these guys back together. Tell us what happened behind the scenes? We were so excited to do it because "vacation" is one of those movies that you don't see over an over all the time. It's not. We don't know a lot about what happened to these guys. You know, that cameron was on tv with. But we know they had a happy ending. There's no tragedies there. They were very happy to see each other. They have gotten together over the years. But just a couple times. And the kids were played by different actors in all of the sequels. Right. But this original cast of "vacation" has remained fairly close and in touch. Anthony michael hall did a little spot on "community," with chevy chase. And when chevy chase got to the photo shoot, he looked around. I think he saw all of the other actors and said, are we here for "caddyshack"? I don't know where his head was that day. That sounds like chevy chase. And "clueless" is tomorrow. "Melrose place" on monday. Thank you, george. A lot of people who have been

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